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Reference Manual
IP2030/RM, Rev AA
Section 4: Getting started
June 2014
Section 4: Getting started80
Standby, Split Off mode relay
This function requires two or more Standby, Split Off Point mode relays. Only one of these
relays is energized at any one time and the others are on standby to take over when needed.
A Standby, Split Off Point relay uses its On Point and Off Point parameters, just like a Set Point
mode relay. A typical application would be emptying a wet well / lift station.
The worked example here illustrates how the function works. To keep the example simple, the
auto-sequencing options are not considered.
Example wet well / lift station application (emptying operation due to rising level)
using standby, split off point relays
Consider an application with two relays, RL1 and RL2, connected to individual pumps in a
wet well. The control unit PV value (D800) is a liquid level measurement in metres.
In Figure 4-39, both Pump 1 and Pump 2 are off because the liquid level is at a
satisfactory level, below 5 m
When the level exceeds 5 m (On Point, P411), relay RL1 is energized to start Pump 1.
(Figure 4-40)
When the level exceeds 8 m (On Point, P421), relay RL2 is energized to start Pump 2.
Relay RL1 is de-energized to switch off Pump 1 (Figure 4-41)
When the level falls to below 5 m (Off point, P422), relay RL2 de-energizes to switch off
Pump 2. Relay RL1 is energized to switch on Pump 1 (Figure 4-42)
In this emptying application, the switch off point for Pump 2 is 5 m; the On Point for
relay 1 P411 (On point, relay RL1) is used. P422 (Off point, relay RL2) is ignored.
When the level falls below 2 m (Off point, P412), relay RL1 de-energizes to switch off
Pump 1
Note
If Pump 1 keeps the level below 8 m, it would stay switched on until the level is 2 m.
Safeguards to prevent overuse of pumps are in “Relay safeguard options” on page 71
Figure 4-39. Both Pump 1 and Pump 2 are off (the level is okay)
5.0 m (P411)
8.0 m (P421)
2.0 m (P412)
Level in m
Pump 1
Pump 2